In recent years, along with the development of the information processing technology such as computers, magnetic recording media such as magnetic disks have been widely used as the external memory devices thereof.
In general, magnetic disks are formed as follows: a non-magnetic backing such as an aluminum alloy backing and glass backing is subjected to a sequence of surface treatments such as a lapping treatment, a polishing treatment and a texture treatment so that the surface becomes rough, and on the non-magnetic backing having the roughened surface is formed a magnetic recording layer, and on this magnetic recording layer is further formed a protective film made from carbon, SiO2, etc.
After forming the protective film, a film cleaning process is carried out to remove protrusions formed on the surface of the protective film and foreign matters on the surface of the magnetic disk. This film cleaning process is generally carried out using an abrasive tape.
Following the cleaning process, a lubricant of fluorocarbon type is applied to to the protective film to form a lubricating film, and burnishing is carried out thereon to remove adhered matter such as dust on the surface of the magnetic recording medium. In general, this burnishing is also carried out by using an abrasive film. Thereafter, these are subjected to predetermined tests so as to produce magnetic recording medium in conformity with the standard.
Conventionally, with respect to films used for film cleaning and burnishing, a lapping film is used comprising abrasive grains such as alumina particles and SiC particles carried on a film made of a material, such as polyethylene terephthalate and polyamide. For example, Japanese Patent Laid-Open Publication No. 85628/1997, 71572/1998 and 114837/1999 have disclosed a lapping film having such a construction.
In recent years, in order to increase the memory capacity of a magnetic disk, the formation technique of protective films has been improved, and a shift has been made from the sputtering method to the chemical vapor deposition (CVD) method. Accordingly, it has become possible to provide a high precision and high quality film with high density and very thin film thickness. Moreover, the surface of the magnetic disk after the film formation becomes more uniform and more clean, thereby making it possible to provide a high quality disk (with less abnormally grown protrusions and reduced number of dust particles generated during the film formation).
Along with the development of the high quality formation film, the lapping film used for film cleaning and burnishing has been improved to meet the change so that the average particle size of abrasive grains used therein, which used to be the level of several μm, has now become more finer grains of not more than 0.3 μm.
However, the lapping film contains hard inorganic particles as an abrasive material, and in the case when irregular protrusions exist on the surface of a lapping film or when grain detachment, etc. occurs therein, the resulting defect is that scratches occur on the surface of the magnetic disk. Moreover, if detached grains remain on the surface of the disk, these grains might cause a serious defect in which they are embedded in the disk in the succeeding process.
Therefore, in recent years when the formation technique of the protective film has been improved, with respect to a film for surface-treating the protective film of a magnetic disk, a function for removing foreign matters by wiping them without causing scratches rather than for polishing the surface of the protective film has come to be required. Moreover, in the case when burnishing is carried out after formation of a lubricating film, the film needs to have an oil-absorbing characteristic in order to remove loose lubricant and render the lubricating film more uniform across the surface of the magnetic disk.
In other words, the quality required for a surface finishing material for the surface of a magnetic disk has come to change in response to the improvement of the film quality and changes in the processes in which it is used, and those materials which cause no scratches and can remove foreign matters and loose lubricant have come to be demanded. That is, although emphasis was put on the polishing function conventionally, emphasis now has been put on the removal of foreign-matter (wiping function).
Japanese Patent Laid-Open Publication No. 66179/1993 discloses a cleaning film for surface-treating a protective film of a magnetic recording medium. This cleaning film is made of a woven cloth with very thin fibers, and this is used for removing dust after the abrasive process using a lapping film. Therefore, it contains no abrasive grains, and causes no scratches on the surface of the magnetic disk. However, the very thin fibers tend to be cut due to tension and friction, and once they are cut, fiber particles come off from the woven cloth. Therefore, the application of this cleaning film instead of the lapping film causes a problem in which the treatment surface is contaminated by fiber. For this reason, cleaning films composed of woven cloth with very thin fibers have not been put into practical use yet as a material for treating a protective film surface of a magnetic recording medium.
The present invention provides a wiping film for removing foreign matter and loose lubricant, without scratching and without depositing fibrous debris on the treatment surface. The wiping film may be used in the treatment of magnetic disks and the like.